3. I heard she was trying to break into his CIA email account.

Broadwell was sending anonymous letters to another woman, threatening her and telling her to keep away from Petreaus.
To send threatening emails is a federal crime so the FBI got involved and tracked down the anonymous emails to Broadwell.

From there they found that she was trying to access Petreaus's CIA email account and at that point it got serious.

So it sounds like a defense attorney might be pretty essential at this point.